This invention relates to supercharger constructions. More specifically, this invention relates to a supercharger wherein a compressor system is driven through an electromagnetically actuated variable slippiing wet clutch to supply boost to an engine according to load requirements. The slipping wet clutch is cooled and lubricated via an isolated or self-contained lubricant flow system.
It is desirable to be able to supply boost energy to an internal combustion engine in the form of compressed air during certain vehicle use conditions such as acceleration from a standing stop. It is also desirable, however, to minimize the parasitic losses which the engine suffers in order to drive boost energy supply systems. In this vein, it is also desirable to be able to completely decouple such systems when engine load conditions will permit effective operation without boost energy augmentation.
A variety of boost energy supply systems have been developed and employed in the past. Each such system is endowed with inherent advantages and shortcomings. As a result, extreme care must be taken to properly match a given engine (having its own capability and requirements) with a boost energy supply system to achieve the desired objective.
Of the boost energy supply systems thus far developed, the following discussed are considered the most noteworthy and exemplary of the alternative approaches.
Positive displacement, constantly engine driven mechanical air pumps, have long been used in conjunction with internal combustion engines to augment or boost the pressure of air supplied to the engines. These systems are typified by the roots blower systems available today in the marketplace. While these systems have many positive advantages, they are nonetheless plagued with certain downside factors, which make them impractical or impossible to use in certain applications, and indeed unacceptable in certain market segments. However, in small passenger car applications, with their ever decreasing engine sizes, the constant parasitic power losses associated with continuously driven mechanical systems, make them intolerable alternatives. Additionally, the excessive noise associated with roots type systems, make them generally unacceptable to the consumer as passenger car power train accessories. On the upside, however, positive displacement pumps require lower specific speeds than centrifugal pumps to supply sufficient mass flow and pressures to a typical reciprocating I-C engine. As such, the speed requirements of positive displacement pumps are more matched to the engine operating speed ranges available, and thus accomplish more efficient and effective boost supplies, than many centrifugal equivalents.
Another approach to mechanically supercharging small passenger car sized, I-C engines, has involved a dynamic system, in which a compressor wheel or its centrifugal equivalent, is constantly driven by the engine to supply the required boost. However, the constant parasitic loss associated with this approach is intolerable for the aforementioned reasons set forth with respect to the roots type systems. Additionally, the high specific speed required for optimum operation of centrifugal compressors, makes them a bad match for direct drive from the engine through clutches and gears.
In one variation of the typical mechanically driven dynamic supercharger system, a control system is provided which allows discrete coupling or de-coupling of the compressor to the engine drive system. However, this variation does not contemplate varying or modulating the speed of the compressor during the driven mode, except as a direct function of engine speed, therefor making it insufficiently versatile to truly match boost augmentation to engine needs in an economical fashion. The mechanically driven supercharger systems described (both positive displacement and centrifugal) do, however, provide nearly instant boost or throttle response to the engine, which is desirable.
Typical turbocharging, which involves exhaust driving of coaxially joined turbine and compressor wheels, to supply boost to an engine, finds ideal application in high exhaust mass flow engine settings. However, even in this setting, the back pressure to the engine, which is naturally associated with inserting a turbine downstream of the engine in the exhaust flow path, presents parasitic losses which can be undesirable. "Turbo-lag", or hesitation, which is involved with turbocharger systems, can also prove undesirable. Todays smaller displacement engines compound the problems of turbocharging to a degree, since they generate substantially less driving exhaust mass flow than their predecessors of yesteryear. As a result of this fact, the development of smaller and smaller turbochargers has been pursued to more properly match the available exhaust mass flow. Still, the turbolag problem has not been eliminated and the back pressure to the engine is still present. On the upside however, turbocharging with the use of exhaust gas bypass systems of the type described in U.S. Pat. No. 4,120,156, issued Oct. 17, 1978, to Charles E. McInerney, allows modulation of the compressor speed and thus the boost to the engine according to load demand and not solely as a function of engine speed and in this vein presents advantages not available to conventional mechanical supercharger users.
The present invention thus marries many of the advantages of turbocharging with those of mechanically supercharging into a single system which minimizes the downside effects of both on the drive system. The method of the present invention thus utilizes the system of the present invention to selectively provide boost to an engine.